The invention relates to a colored luminaire, in particular a colored signaling light for automobiles, provided with a lamp and a luminaire cover inside which the lamp has a bulb with a coating of a layer comprising an organic pigment.
Colored luminaires are used in automobiles in various locations, for example for brake lights, indicator lights, and fog lights. In conventional colored luminaires, the bulb of the lamp is made from colorless glass, and the lamp is positioned under a colored, usually red or yellow luminaire cover. A more recent development involves the use of colored lamps for colored luminaires under a colorless or neutrally colored cover. This renders it possible to incorporate signaling lamps of various types as a group of lamps under one and the same luminaire cover.
Luminaires with colored lamps under a colorless or neutrally colored cover have the advantage that they render possible a flexible, optically attractive design for integrated front and rear luminaires. In addition, they are cheaper than luminaires with multiple housings or covers of various colors. These luminaires in addition are safer in traffic because the difference between switched-on and switched-off lights is more clearly noticeable in daylight in the case of luminaires having colored lamps and a colorless or neutrally colored luminaire cover.
In principle, inorganic or organic color pigments may be used for the colored, pigmented bulb coating of colored lamps. The known red and yellow inorganic color pigments are stable in the long term, but they do not have optimum colorimetric values. Bulb coatings with organic color pigments, for example the coatings with red pigments from the group of anthrachinon pigments known from JP-A-60 116958, can indeed be optimized as regards their color co-ordinates, but they tend towards the yellow in time.
As in many other branches of industry, the trend in the case of automobile lamps is towards an ever increasing miniaturization. Efforts are made to reduce the overall dimensions of the lighting units of an automobile and, for example, to integrate the signaling lights into the main lights. The lamps in such lighting units, however, are subjected to higher thermal loads.
It is an object of the present invention to provide a colored luminaire fitted with a lamp and a luminaire cover in which the lamp has a bulb with a coating of a layer comprising an organic color pigment, which lamp has a long useful life also at elevated ambient temperatures as well as optimized color co-ordinates, and which lamp is suitable for an automobile lighting unit.
According to the invention, this object is achieved by means of a colored luminaire fitted with a lamp and a luminaire cover wherein the lamp has a bulb coating with a first layer comprising a pigment, which pigment is chosen from a group comprising perylene pigments, perinone pigments, isoindoline pigments, and thioindigo pigments.
A luminaire with such a lamp has a long useful life. It is not attacked by UV radiation, moisture, and spray salt and is resistant to temperatures of between 250 and 350xc2x0 C. Colored luminaires with bulb coatings comprising these pigments alone or in combination with further pigments for color correction comply with the color standards for automobile lights as defined by the E.C.E. for Europe and the S.A.E. for the USA.
In a preferred embodiment, the first pigment-containing layer in addition comprises an iron oxide pigment. An iron oxide pigment in the layer corrects the color value of the organic pigment, for example in the bluish range, for example from yellow to amber, or from orange/red to red. If the lamp is exposed to temperatures above 250xc2x0 C. for a longer period in the luminaire, it will still have emergency running properties.
It may be preferable that the first pigment-containing layer comprises an iron oxide pigment and a silicon-oxygen compound. Such a layer adheres very well to the glass of the lamp bulb.
In a further preferred embodiment of the invention, a second pigment-containing layer is arranged between the bulb and the first pigment-containing layer, which second layer comprises an iron oxide pigment. If the lamp is exposed to strong and frequent temperature changes and the upper layer should flake off, this embodiment of the luminaire also has emergency running properties.
A transparent layer comprising a silicon-oxygen compound may be arranged between the bulb and the first pigment-containing layer. The mechanical strength of the coating is improved thereby.
It is also possible that the lamp comprises a transparent covering layer comprising a silicon-oxygen compound so as to improve the scratch resistance of the pigment-containing coating.
The invention also relates to a lamp with a bulb having a coating of a layer comprising a pigment chosen from a group which comprises the perylene pigments, perinone pigments, isoindoline pigments, and thioindigo pigments.
The invention will be explained in more detail below with reference to three embodiments.
A colored luminaire according to the invention is provided with a lamp and a luminaire cover inside which the lamp is present and comprises a bulb with a coating of a layer comprising a pigment chosen from the group of the perylene pigments, perinonepigments, isoindoline pigments, and thioindigo pigments.
Depending on the construction of the lamp, the coating may be provided on one or several walls of the lamp bulb, both on the inside and on the outside of the bulb.
The colored luminaire may in addition be fitted with other components, for example means for fastening the lamp in the luminaire, protection means against dust, damage, and moisture, as well as the components necessary for power supply, for example lampholders, cables, ballasts, starters, ignition devices, and connection terminals. A desired light distribution and a dazzle limitation may be achieved by means of optical reflectors, clear or frosted closing plates, rasters of metal or synthetic resin, scattering glass plates, and prismatic reflectors. In an embodiment of the invention, the luminaire contains two or more colored lamps under a joint luminaire cover which is colorless or neutrally colored.
Perylene, perinone, isoindoline, or thioindigo pigments are used for the first pigment-containing layer. The pigments used are polycyclical pigments which have been known for a longer time for coloring textile fibers. The pigments will be denoted hereinafter in accordance with their chemical structures or their color index (C.I.) as published jointly by Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists.
Perinones [CAS 4424-06-0 (trans-perinone), CAS 4216-02-8 (cis-perinone)] are derivatives of 1,4,5,8-naphthalenetetracarbonic acid. Cis- and trans-perinone are obtained as a cis/trans isomer mixture through heating of 1,4,5,8-naphthalenetetracarbonic acid in the form of its monoanhydride, for example in glacial acetic acid at 120xc2x0 C., with o-phenylenediamine. When the isomers are separated, the trans-perinone is obtained with a pure orange-yellow color and the cis-perinone with a red color.
The perylene pigments are derivatives of 3,4,9,10-perylenetetracarbonic acid. Preferably used may be: the reddish yellow and yellow pigments perylenetetracarbonic-acid bis(methylimide) PR 179 (CAS 5521-31-3), perylenetetracarbonic-acid dianhydride PR 224 (CAS 3049-71-6), bis-dimethylphenylperylimide PR 149, and perylenetetracarbonic-acid diimide) PV 29 (CAS 81-33-4). Generally, the perylene pigments are manufactured from 3,4,9,10-perylenetetracarbonic-acid anhydride through conversion with primary aliphatic amines or substituted anilines, possibly in the presence of a catalyst.
The isoindoline pigments have as their central structural element an isoindoline ring which may be substituted with various substituents via a Cxe2x95x90C double bond. Depending on the substituent, the isoindoline pigments are yellow, orange, or red in color. PY 139 (CAS 36888-99-0) with the general formula C16H9N5O6 has an orange color and is thermally highly stable. PY 185 (CAS 76199-85-4) has a yellow color and is also thermally very stable.
Of the thioindigo pigments, it is especially the derivatives substituted with chlorine and/or methyl groups which are suitable for the invention. Tetrachloroorthoindigo PR 88 (CAS 14295-43-3) has a reddish violet color which is suitable for adjusting the color of other red pigments.
Preferably, the perylene, perinone, isoindoline, or thioindigo pigments are used in a fine-grain, colloidal form with a particle size 2 nm less than d less than 200 nm so as to obtain transparent layers.
In a preferred embodiment of the invention, the first pigment-containing layer may contain an iron oxide pigment in addition to the perylene, perinone, isoindoline, and thioindigo pigments.
Iron oxide pigments have a wide color spectrum from yellow via orange to red, brown, and black. The natural and synthetic iron oxide pigments used consist of well-defined compounds of known crystal structure. xcex1-Fe2O3 (haematite) with a corundum structure changes its color in dependence on its particle size and crystal shape from bright red to dark violet. xcex3-Fe2O3 (maghemite) with spinel structure is brown. xcex1-FeOOH (goethite) with diaspore structure changes its color from bright yellow to brownish yellow as its particle size increases. xcex3-FeOOH (lepidocrocite) with boehmite structure changes its color from yellow to orange as the particle size increases. These iron oxides are iron(III) oxides. The reddish violet to black Fe3O4 (magnetite) with spinel structure is suitable in exceptional cases only. Preferred iron oxide pigments are those which are transparent in fine-grain, colloidal form with a particle size 2 nm less than d less than 15 nm so as to obtain transparent layers.
Transparent yellow iron oxide C. I. PY 42:77492 is xcex1-FeOOH (goethite) with diaspore structure. When heated, it changes into the transparent brownish red xcex1-Fe2O3 (haematite) C. I. PR 101:77491, which is preferably used. Orange intermediate hues develop upon a short temperature treatment. They may also be obtained through mixing of yellow and red pigments. The iron oxide pigments with a particle size 2 nm less than d less than 200 nm are preferred.
It is also possible for the first pigment-containing layer to comprise a silicon-oxygen compound, for example amorphous or crystalline silicon dioxide, quartz, a silica gel, or a silicic acid or silicate, i.e. salts or esters of the silicic acids, in particular tetraethylorthosilicate (TEOS), a silicone, or a siloxane.
The pigments and the silicon-oxygen compounds may be applied in a single color layer.
In an alternative embodiment of the invention, the colored bulb coating may have a variable multiple layer construction. It always comprises a first colored layer which comprises a pigment chosen from the group of the perylene pigments, perinone pigments, isoindoline pigments, and thioindigo pigments.
Below the first colored layer, a layer comprising an iron oxide may first be provided on the lamp bulb. The layer comprising an iron oxide may contain the iron oxide either as a fine-grain pigment or as a deposit from a sol-gel process. If the iron oxide is provided as a pigment, both a dry, for example electrostatic, deposition and a wet deposition, for example as a watery suspension by means of dipping or spraying, are possible.
In another embodiment of the invention, the multiple layer construction for the coating of the lamp bulb is such that first a layer comprising an iron oxide is provided on the inside or outside of the lamp bulb. The iron oxide for this layer may either be provided as a fine-grain pigment or in a sol-gel process. A temperature-resistant, transparent protective layer comprising a silicon-oxygen compound, for example a layer of SiO2 or of quartz glass, is provided over the layer comprising iron oxide. The pigment-containing layer is then provided over this assembly.
In a further embodiment of the invention, the multiple layer construction for the coating of the lamp bulb is such that a transparent layer comprising a silicon-oxygen compound is arranged between the bulb and the first pigment-containing layer.
A temperature-resistant, transparent covering layer may be arranged over the pigment-containing layers. The covering layer comprises a silicon-oxygen compound, for example amorphous or crystalline silicon dioxide, quartz, a silica gel, or a silicic acid or a silicate, i.e. salts or esters of the silicic acids, in particular tetraethylorthosilicate (TEOS). Alternatively, this additional covering layer may also be a temperature-resistant, transparent, colorless or colored varnish or a transparent ceramic layer, for example of Al203 or enamel. If the layers are provided on the inside of the bulb, the covering layer will prevent a chemical change in the pigments. If the coating is provided on the outside, the covering layer provides a scratch-proof surface which renders further processing of the bulb in lamp manufacture easier.
Preferably, a covering layer with a suitable refractive index is used which reduces the scattering caused by the layers containing pigments.
Conventional methods for coating substrates of complicated shape may be used as methods for applying the coating on the lamp bulbs. These include wet coating methods such as, for example, spraying, dipping, and brushing. Dry coating methods, for example electrostatically supported dusting, are suitable for providing the pigmented coating on the lamp bulb.
The pigments are to be dispersed in water, an organic solvent, or a binder mixture, possibly together with a dispersing agent, a surfactant, and an anti-foaming agent in the case of wet coating methods. Suitable binder mixtures for a luminaire according to the invention are organic or inorganic binders which withstand an operating temperature of 250xc2x0 C. to 350xc2x0 C. without decomposition, brittling, or discoloration.
A layer thickness from 0.5 to 2.0 xcexcm may be sufficient for layers which contain pigments and which are free from binders. Layers containing binders in general have a layer thickness of 1 to 50 xcexcm.
The pigment-coated lamps were subjected to an accelerated temperature endurance test in which the lamps were kept permanently at 300xc2x0 C. The color point showed only a minimal shift within the range laid down by the E.C.E and the S.A.E. for the color specification during a period of 150 h. The color point also remained within the E.C.E. color specification during normal lamp operation for a period of 500 h.